Somatosensory functions – pain research (Torebjörk, Schmidt): Studies
of sensory functions in man had earlier been restricted since it was not possible
to record signals from cutaneous sensory endings in humans. Torebjörk
showed in his thesis that is was possible to study even unmyelinated C fibres.
The technique was improved when Torebjörk and Ochoa introduced the so
called intraneural microstimulation by which it was possible to study the
correlation between impulse characteristics and subjective sensation. Microneurography
from human skin nerves combined with the technique of intraneural microstimulation
has made it possible to analyse the specific types of sensations aroused by
neural impulse messages signalled by various types of A- and C-fibre sensory
units. Studies of this type have been made both in healthy subjects and in
patients with different types of paraestesias, hyperalgesias and neurogenic
pain. Two types of C-nociceptors have been identified: polymodal units and
mechanosensitive units activated by algogenic substances. A special type of
C-units are histamine responsive and give rise not to pain but to itch sensations.
The technique allows differentiation between chronic pain syndromes due to
peripheral nociceptor hyperexitability or due to increased responsivness of
central sensory neurones.